1. Field of the Invention
The present invention relates to a wheel supporting apparatus capable of a smooth and small turn at a large steering angle and having a large rigidity against a bending moment at a wheel supporting part.
2. Description of the Prior Art
In general, four wheels are required to have a same turning center for a smooth turn of a four-wheeled vehicle. For this purpose, conventional steering mechanisms have employed steering link mechanisms provided with, for instance, knuckle arms and tie rods.
In this steering link mechanism, as shown in FIG. 3, tie rods 01 are rotatably connected at tie rod ends 01a to ends of knuckle arms 02, of which other ends are connected to king pins 03 of right and left wheels, respectively. Each tie rod 01 in this steering mechanism is adapted to be moved laterally or in right and left directions by a steering torque applied from a steering wheel through, for instance, a rack-and-pinion gear, a worm gear or a hydraulic cylinder so as to turn the knuckle arm 02. In this manner, the right and left wheels are laterally steered.
In many conventional automobiles, as shown in FIG. 4, each front wheel 04 is supported by a suspension 05 of a strut type. In this arrangement, a knuckle arm 6 which forms a part of a steering mechanism for the front wheel 4 is formed integrally with a strut 05a, so that the strut 05a is turned together with it when the wheel 4 is steered for turning the vehicle,
However, in such steering mechanism, the tie rod 01 and the knuckle arm 02 may be rectilinearly aligned to each other, as shown in FIG. 3, in which case further steering operation for the wheels cannot be carried out. This condition is a limit of allowable wheel steering operation and a limit value of a steering angle .alpha. is generally about 45 degrees. The limit in the wheel steering will restrict the steering operation for small turns.
Further, if the apparatus were designed to set the steering angle .alpha. of the wheels to a value exceeding the limit, e.g., 90 degrees, such a problem would be caused that the wheels could not be driven by a driving power from a driving source provided on a vehicle body at the steering angle .alpha. of 90 degrees.
In view of the above, the applicant has already filed the Japanese Patent Application No. 63-165498 for a steering mechanism and a vehicle provided with the same, in which the above problems are resolved.
In the steering mechanism and the vehicle provided with the same disclosed in this patent application, the steering angle of the steering wheel is mechanically transmitted to the wheels through a link mechanism in such a manner that the velocity of the steering angle is increased by a velocity increasing gear provided at the vehicle frame, and driving motors are individually associated with the respective wheels.
Further, in the wheel supporting structures in this patent application, a steering shaft is fixed to a casing of a wheel driving motor associated with each wheel, and the steering shaft is supported by the vehicle frame to be rotatable around a center axis of the steering shaft.
Usage of the velocity increasing gear for each wheel enables steering operation of the wheel over 90 degrees around the steering shaft as well as rotational driving by the driving motors at a steering angle of 90 degrees.
The steering mechanism thus employing the velocity increasing gear may be used for each of the front and rear wheels, in which case the front wheels as well as the rear wheels may be steered at 90 degrees, which enables a small turn and a parallel movement in a lateral direction.
In this wheel supporting structure, there is a considerably long distance between a wheel grounding point and a point at which the steering shaft is supported by the vehicle frame. Therefore, when the wheel receives forces in the lateral and longitudinal directions during the steering operation and others, a large moment is generated, and a bending force caused by this bending moment is concentrated in the supporting part of the vehicle frame and the steering shaft. For this reason, the supporting part of the vehicle frame and the steering shaft may not have sufficient rigidity against this bending force.
Accordingly, it is an object of the invention to provide a wheel supporting apparatus, overcoming the above-noted problems, in which a large steering angle can be set, a small turn and a parallel movement can be smoothly and surely achieved, and further a sufficient rigidity can be obtained against bending forces which is caused by a bending force in a longitudinal direction, i.e., forward and backward directions, applied to the wheels.